1. Field of the Invention
The present invention relates to an image processing apparatus, an image noise detecting method, and a computer-readable recording medium.
2. Description of the Related Art
Conventionally performed is document scanning using an image processing apparatus, such as a multifunction peripheral (MFP), to perform copying, facsimile transmission, distribution of image data over a network, and the like. Such an image processing apparatus generates image data by conveying a document to be scanned using an automatic document feeder (ADF), illuminating the document being conveyed with light, and receiving light reflected from the document with a charge coupled device (CCD) image sensor. However, this type of image processing apparatus can undesirably produce image noise such as streaks (hereinafter, “streak image noise”) extending in the sub-scanning direction in image data generated by scanning when document scanning is performed with dust on an optical path of scanning light that is to be received by the CCD image sensor.
In this regard, various techniques for detecting such streak image noise that can be produced during scanning have been proposed. For instance, Japanese Patent Application Laid-open No. 2008-99129 discloses an image reading apparatus that detects streak image noise extending in the sub-scanning direction. When noise is detected in pixels on a series of three main-scanning lines that are contiguous in the sub-scanning direction, this image reading apparatus determines that these lines have streak image noise extending in the sub-scanning direction.
However, other image noise than the streak image noise can be produced in image data during document scanning when the image data is generated by scanning. Examples of the other image noise include dotted image noise which is interspersed minute image noise. The image processing apparatus that uses the conventional detection technique described above does not take an influence by such other image noise into account. Accordingly, the image processing apparatus can possibly mistake such other image noise for streak image noise. Furthermore, when dotted image noise is produced in image data, density contrast between streak image noise and the dotted image noise becomes small as illustrated in FIG. 7. This disadvantageously lowers detection accuracy of the streak image noise.
Therefore, there is a need for an image processing apparatus capable of highly-accurate detection of streak image noise resulting from dust on an optical path of scanning light unaffected by other image noise that can be produced during document scanning.